Transitional metal hydroxides generally have been produced by adding an alkaline solution to a solution of a water soluble transition metal salt which results in the precipitation of the metal hydroxide. Metal hydroxides have been found to be useful in a variety of applications. For example, manganese hydroxide has been used as a pigment in the ceramic and refractories industries. Copper hydroxide and cobalt hydroxide have been used as pigments and in paints. Metal hydroxides also are useful as intermediates in the preparation of other metal compounds. For example, the transition metal hydroxides can be used as a starting material for preparing overbased and complex metal carboxylates containing varying amounts of the transition metal which are useful as lubricating oil additives, anti-knock agents for gasoline, fuel additive type combustion improvers, smoke or toxic fume suppressants, driers and ultraviolet co-catalysts for inks and coatings.
As mentioned above, the prior art method for preparing metal hydroxides such as the transition metal hydroxides involves the addition of an alkaline solution to a transition metal salt solution whereupon the transition metal hydroxide is precipitated with the formation of a new salt. The soluble transition metal salts include the chlorides, sulfates, nitrates and acetates. Alkaline solutions which have been utilized include sodium hydroxide, potassium hydroxide and ammonium hydroxide. In USSR 548,570, cobalt hydroxide is obtained by treating cobalt basic carbonate with sodium hydroxide. The use of the basic carbonate is reported to result in precipitation of the hydroxide at normal temperatures and with reduced contamination. An apple-green precipitate of nickel hydroxide is obtained when potassium or sodium hydroxide is added to a solution of a nickelous salt such as nickel nitrate or nickel ammonium nitrate.
One of the difficulties of the prior art method for preparing transition metal hydroxides is the concurrent formation of an alkali metal salt such as sodium chloride, potassium chloride, sodium sulfate, sodium nitrate, sodium acetate, etc., depending upon the anion present in the soluble transition metal salt. Accordingly, it has been difficult to prepare transition metal hydroxides which are free of alkali metal salt impurities. The prior art methods also are more costly since the initial metal salts must be prepared, often from corrosive chemicals such as nitric or sulfuric acids. Since the prior art method described above results in the formation of salts, there also is a disposal problem created.